If a prospectus is issued with an untrue statement included in it, any person who authorised the issue of the prospectus is guilty of an offence and liable to imprisonment or a fine, or both, unless he proves either—
that the statement was immaterial, or
that he had reasonable ground to believe and did, up to the time of the issue of the prospectus, believe that the statement was true.
A person is not deemed for purposes of this section to have authorised the issue of a prospectus by reason only of his having given the consent required by section 61 to the inclusion in it of a statement purporting to be made by him as an expert.